Mutations in JAGGED1 gene are predominantly sporadic in Alagille syndrome

Investigation of cryptic JAG1 splice variants as a cause of Alagille syndrome and performance evaluation of splice predictor tools

Haploinsufficiency of JAG1 is the primary cause of Alagille syndrome (ALGS), a rare, multisystem disorder. The identification of JAG1 intronic variants outside of the canonical splice region as well as missense variants, both of which lead to uncertain associations with disease, confuses diagnostics. Strategies to determine whether these variants affect splicing include the study of patient RNA or minigene constructs, which are not always available or can be laborious to design, as well as the utilization of computational splice prediction tools. These tools, including SpliceAI and Pangolin, use algorithms to calculate the probability that a variant results in a splice alteration, expressed as a Δ score, with higher Δ scores (>0.2 on a 0-1 scale) positively correlated with aberrant splicing. We studied the consequence of 10 putative splice variants in ALGS patient samples through RNA analysis and compared this to SpliceAI and Pangolin predictions. We identified eight variants with aberrant splicing, seven of which had not been previously validated. Combining these data with non-canonical and missense splice variants reported in the literature, we identified a predictive threshold for SpliceAI and Pangolin with high sensitivity (Δ score >0.6). Moreover, we showed reduced specificity for variants with low Δ scores (<0.2), highlighting a limitation of these tools that results in the misidentification of true splice variants. These results improve genomic diagnostics for ALGS by confirming splice effects for seven variants and suggest that the integration of splice prediction tools with RNA analysis is important to ensure accurate clinical variant classifications.

Clinical, pathological and genetic characteristics of 17 unrelated children with Alagille Syndrome

BACKGROUND

Alagille syndrome (ALGS) is a multisystem genetic disorder frequently characterized by hepatic manifestations. This study analyzed the clinical, pathological, and molecular genetic features of ALGS to improve the efficiency of clinical diagnosis.

METHODS

We retrospectively analyzed the clinical manifestations, pathological examination findings, and genetic testing results of 17 children diagnosed with ALGS based on the revised criteria and hospitalized at our center from January 2012 to January 2022.

RESULTS

The clinical manifestations are as follows: Cholestasis (16/17, 94%), characteristic facies (15/17, 88%), heart disease (12/16, 75%), butterfly vertebrae (12/17, 71%) and posterior embryotoxon (7/12, 58%). Among the 15 patients who underwent liver pathology examination, 13 (87%) were found to have varying degrees of bile duct paucity. Genetic testing was performed on 15 children, and pathogenic variants of the jagged canonical Notch ligand 1 (JAG1) gene were identified in 13 individuals, including 4 novel variants. No pathogenic variant in the notch homolog 2 (NOTCH2) gene were identified, and 2 children exhibited none of the aforementioned gene pathogenic variants. The median follow-up duration was 7 years. Of the remaining 15 patients (excluding 2 lost to follow-up), 11 remained stable, 4 deteriorated, and no patient died during the follow-up period.

CONCLUSIONS

Among children diagnosed with ALGS, cholestasis stands as the most common feature. To minimize the risk of misdiagnosis, genetic testing should be performed on children exhibiting cholestasis, followed by the application of the revised diagnostic criteria for ALGS. While pharmacological therapy has shown effectiveness for ALGS patients, liver transplantation may be considered in instances of severe pruritus.

Functional characterization of 2,832 JAG1 variants supports reclassification for Alagille syndrome and improves guidance for clinical variant interpretation

Pathogenic variants in the JAG1 gene are a primary cause of the multi-system disorder Alagille syndrome. Although variant detection rates are high for this disease, there is uncertainty associated with the classification of missense variants that leads to reduced diagnostic yield. Consequently, up to 85% of reported JAG1 missense variants have uncertain or conflicting classifications. We generated a library of 2,832 JAG1 nucleotide variants within exons 1-7, a region with a high number of reported missense variants, and designed a high-throughput assay to measure JAG1 membrane expression, a requirement for normal function. After calibration using a set of 175 known or predicted pathogenic and benign variants included within the variant library, 486 variants were characterized as functionally abnormal (n = 277 abnormal and n = 209 likely abnormal), of which 439 (90.3%) were missense. We identified divergent membrane expression occurring at specific residues, indicating that loss of the wild-type residue itself does not drive pathogenicity, a finding supported by structural modeling data and with broad implications for clinical variant classification both for Alagille syndrome and globally across other disease genes. Of 144 uncertain variants reported in patients undergoing clinical or research testing, 27 had functionally abnormal membrane expression, and inclusion of our data resulted in the reclassification of 26 to likely pathogenic. Functional evidence augments the classification of genomic variants, reducing uncertainty and improving diagnostics. Inclusion of this repository of functional evidence during JAG1 variant reclassification will significantly affect resolution of variant pathogenicity, making a critical impact on the molecular diagnosis of Alagille syndrome.

Alagille syndrome: understanding the genotype-phenotype relationship and its potential therapeutic impact

INTRODUCTION

Alagille syndrome (ALGS) is an autosomal dominant, multisystem genetic disorder with wide phenotypic variability caused by mutations in the Notch signaling pathway, specifically from mutations in either the Jagged1 (JAG1) or NOTCH2 gene. The range of clinical features in ALGS can involve various organ systems including the liver, heart, eyes, skeleton, kidney, and vasculature. Despite the genetic mutations being well-defined, there is variable expressivity and individuals with the same mutation may have different clinical phenotypes.

AREAS COVERED

While no clear genotype-phenotype correlation has been identified in ALGS, this review will summarize what is currently known about the genotype-phenotype relationship and how this relationship influences the treatment of the multisystemic disorder. This review includes discussion of numerous studies which have focused on describing the genotype-phenotype relationship of different organ systems in ALGS as well as relevant basic science and population studies of ALGS. A thorough literature search was completed via the PubMed and National Library of Medicine GeneReviews databases including dates from 1969, when ALGS was first identified, to February 2023.

EXPERT OPINION

The genetics of ALGS are well defined; however, ongoing investigation to identify genotype-phenotype relationships as well as genetic modifiers as potential therapeutic targets is needed. Clinicians and patients alike would benefit from identification of a correlation to aid in diagnostic evaluation and management.

Clinical and Genetic Characteristics of Alagille Syndrome in Adults

BACKGROUND AND AIMS

Alagille syndrome (AGS) is an autosomal dominant multisystem disorder caused by mutations in the JAG1 and NOTCH2 genes. AGS has been rarely reported in adult patients, mainly because its characteristics in adults are subtle. The study aimed to improve the understanding of adult AGS by a descriptive case series.

METHODS

Eight adults diagnosed with AGS at our hospital between June 2016 and June 2019 were included in the study. Clinical data, biochemical results, imaging results, liver histopathology, and genetic testing were analyzed.

RESULTS

Three female and five male patients with a median age of 24.5 years at the time of diagnosis were included in the analysis. The clinical manifestations were adult-onset (62.5%, 5/8), cholestasis (50%, 4/8), butterfly vertebrae (62.5%, 5/8), systolic murmurs (12.5%, 1/8), typical facies (12.5%, 1/8), posterior embryotoxon, and renal abnormalities (0/8). Genetic sequencing showed that all patients had mutations, with four occurring in the JAG1 gene and four in the NOTCH2 gene. Six were substitution mutations, one was a deletion mutation, and one was a splicing mutation. Five had been previously reported; but the others, one JAG1 mutation and two NOTCH2 mutations were unique and are reported here for the first time.

CONCLUSIONS

The clinical manifestations highlighted by the current diagnostic criteria for most adults with AGS are atypical. Those who do not meet the criteria but are highly suspicious of having AGS need further evaluation, especially genetic testing.

Different clinical and genetic features of Alagille patients with progressive disease versus a jaundice-free course

Background and Aim

Alagille syndrome (ALGS) is a multisystem disorder with variable clinical courses. This study investigated the clinical and genetic features of ALGS patients with different outcomes and analyzed the liver pathology at liver transplantation (LT) compared with that in biliary atresia (BA).

Methods

We report the clinical characteristics, outcomes, and genetic mutations of 25 children with ALGS followed for a median of 7.3 years. Patients were classified into (i) jaundice-free (JF) group (resolving jaundice after 2 years of age); (ii) progressive disease (PD) group (persistent jaundice or progressive cholestasis). In addition, we analyzed the explant liver in 10 ALGS patients compared with 20 age-matched BA patients at the time of LT.

Results

Nine patients (36%) in the JF group had a favorable outcome, with longer native liver survival than patients with PD (n = 16, P < 0.001). Fourteen of the PD group patients received LT or died. We identified 18 different JAG1 mutations in 22 patients. Three unrelated probands in the JF group had the same de novo mutation in JAG1, c.2122-2125delCAGT. Compared with BA children, ALGS patients had lower METAVIR scores in liver pathology, higher serum albumin levels, and lower weight-for-age z-scores when receiving LT.

Conclusion

One-third of ALGS patients had JF and a favorable course. Children with ALGS presenting with persistent jaundice beyond 2 years of age should be cautioned for poor prognosis. ALGS patients tend to have a lesser extent of cirrhosis, and more growth problems than BA patients at the time of LT.

Broadening the clinical spectrum of ALGS: an Egyptian cohort with five novel mutations in JAG1 gene

Background

Alagille syndrome (ALGS) is a rare autosomal dominant multisystem disorder that affects the liver, heart, eyes, vertebrae, and kidneys and is associated with characteristic facies. This work aimed to study the spectrum of the clinical features of ALGS in an Egyptian cohort of patients in conjunction with partial sequencing of the JAG1 gene.

Methods

This study included 17 pediatric ALGS patients diagnosed on clinical grounds: facial features, cholestatic liver disease, and cardiac, vertebral, and ocular findings. Molecular analysis was conducted in 10 selected exons of the JAG1 gene.

Results

The clinical features of ALGS included cholestatic liver disease (100%), facial dysmorphism (100%), cardiac abnormalities (88.2%), butterfly vertebrae (64.7%), posterior embryotoxon (35.2%), poor growth (41%), xanthomata (11.8%), and hiatus hernia (11.8%). Five novel pathogenic JAG1 mutations were identified in this study, including two nonsense mutations, one splicing mutation, one frameshift insertion, and one frameshift deletion. In two patients, the mutations were confirmed to be de novo, as the mutations could not be detected in both parents.

Conclusion

Five novel JAG1 pathogenic variants were identified in this study. This is the first molecular study to report pathogenic mutations in the JAG1 gene within an Egyptian cohort of children with ALGS.

Role of YAP1 Signaling in Biliary Development, Repair, and Disease

Yes-associated protein 1 (YAP1) is a transcriptional coactivator that activates transcriptional enhanced associate domain transcription factors upon inactivation of the Hippo signaling pathway, to regulate biological processes like proliferation, survival, and differentiation. YAP1 is most prominently expressed in biliary epithelial cells (BECs) in normal adult livers and during development. In the current review, we will discuss the multiple roles of YAP1 in the development and morphogenesis of bile ducts inside and outside the liver, as well as in orchestrating the cholangiocyte repair response to biliary injury. We will review how biliary repair can occur through the process of hepatocyte-to-BEC transdifferentiation and how YAP1 is pertinent to this process. We will also discuss the liver's capacity for metabolic reprogramming as an adaptive mechanism in extreme cholestasis, such as when intrahepatic bile ducts are absent due to YAP1 loss from hepatic progenitors. Finally, we will discuss the roles of YAP1 in the context of pediatric pathologies afflicting bile ducts, such as Alagille syndrome and biliary atresia. In conclusion, we will comprehensively discuss the spatiotemporal roles of YAP1 in biliary development and repair after biliary injury while describing key interactions with other well-known developmental pathways.

Sequencing of a Chinese tetralogy of fallot cohort reveals clustering mutations in myogenic heart progenitors

Tetralogy of Fallot (TOF) is the most common cyanotic heart defect, yet the underlying genetic mechanisms remain poorly understood. Here, we performed whole-genome sequencing analysis on 146 nonsyndromic TOF parent-offspring trios of Chinese ethnicity. Comparison of de novo variants and recessive genotypes of this data set with data from a European cohort identified both overlapping and potentially novel gene loci and revealed differential functional enrichment between cohorts. To assess the impact of these mutations on early cardiac development, we integrated single-cell and spatial transcriptomics of early human heart development with our genetic findings. We discovered that the candidate gene expression was enriched in the myogenic progenitors of the cardiac outflow tract. Moreover, subsets of the candidate genes were found in specific gene coexpression modules along the cardiomyocyte differentiation trajectory. These integrative functional analyses help dissect the pathogenesis of TOF, revealing cellular hotspots in early heart development resulting in cardiac malformations.

Alagille Syndrome: A Focused Review on Clinical Features, Genetics, and Treatment

Alagille syndrome (ALGS) is an autosomal dominant disorder caused by pathogenic variants in JAG1 or NOTCH2, which encode fundamental components of the Notch signaling pathway. Clinical features span multiple organ systems including hepatic, cardiac, vascular, renal, skeletal, craniofacial, and ocular, and occur with variable phenotypic penetrance. Genotype-phenotype correlation studies have not yet shown associations between mutation type and clinical manifestations or severity, and it has been hypothesized that modifier genes may modulate the effects of JAG1 and NOTCH2 pathogenic variants. Medical management is supportive, focusing on clinical manifestations of disease, with liver transplant indicated for severe pruritus, liver synthetic dysfunction, portal hypertension, bone fractures, and/or growth failure. New therapeutic approaches are under investigation, including ileal bile acid transporter (IBAT) inhibitors and other approaches that may involve targeted interventions to augment the Notch signaling pathway in involved tissues.

Characterization of the Spectrum of Ophthalmic Changes in Patients With Alagille Syndrome

Purpose

The purpose of this study was to characterize the phenotypic spectrum of ophthalmic findings in patients with Alagille syndrome.

Methods

We conducted a retrospective, observational, multicenter, study on 46 eyes of 23 subjects with Alagille syndrome. We reviewed systemic and ophthalmologic data extracted from medical records, color fundus photography, fundus autofluorescence, optical coherence tomography, visual fields, electrophysiological assessments, and molecular genetic findings.

Results

Cardiovascular abnormalities were found in 83% of all cases (of those, 74% had cardiac murmur), whereas 61% had a positive history of hepatobiliary issues, and musculoskeletal anomalies were present in 61% of all patients. Dysmorphic facies were present in 16 patients, with a broad forehead being the most frequent feature. Ocular symptoms were found in 91%, with peripheral vision loss being the most frequent complaint. Median (range) Snellen visual acuity of all eyes was 20/25 (20/20 to hand motion [HM]). Anterior segment abnormalities were present in 74% of the patients; of those, posterior embryotoxon was the most frequent finding. Abnormalities of the optic disc were found in 52%, and peripheral retinal abnormalities were the most frequent ocular finding in this series, found in 96% of all patients. Fifteen JAG1 mutations were identified in 16 individuals; of those, 6 were novel.

Conclusions

This study reports a cohort of patients with Alagille syndrome in which peripheral chorioretinal changes were more frequent than posterior embryotoxon, the most frequent ocular finding according to a number of previous studies. We propose that these peripheral chorioretinal changes are a new hallmark to help diagnose this syndrome.

Two Novel Mutations in the JAG1 Gene in Pediatric Patients with Alagille Syndrome: The First Case Series in Czech Republic

Background: Alagille syndrome (ALGS) is a highly variable multisystem disorder inherited in an autosomal dominant pattern with incomplete penetration. The disorder is caused by mutations in the JAG1 gene, only rarely in the NOTCH2 gene, which gives rise to malformations in multiple organs. Bile duct paucity is the main characteristic feature of the disease. Methods: Molecular-genetic examination of genes JAG1 and NOTCH2 in four probands of Czech origin who complied with the diagnostic criteria of ALGS was performed using targeted next-generation sequencing of genes JAG1 and NOTCH2. Segregation of variants in a family was assessed by Sanger sequencing of parental DNA. Results: Mutations in the JAG1 gene were confirmed in all four probands. We identified two novel mutations: c.3189dupG and c.1913delG. Only in one case, the identified JAG1 mutation was de novo. None of the parents carrying JAG1 pathogenic mutation was diagnosed with ALGS. Conclusion: Diagnosis of the ALGS is complicated due to the absence of clear genotype-phenotype correlations and the extreme phenotypic variability in the patients even within the same family. This fact is of particular importance in connection to genetic counselling and prenatal genetic testing.

Long-term follow-up of a patient with JAG1-associated retinopathy

PURPOSE

To report the long-term structural and functional changes in the posterior segments of an adult with an unusual retinal dystrophy caused by a novel mutation in JAG1.

METHODS

A 33-year-old female underwent comprehensive ophthalmic examination, including best corrected visual acuity (BCVA) measurement, dilated fundus imaging (wide-angle fundus colour and short wavelength autofluorescence imaging), macular and peripheral spectral-domain optical coherence tomography (SD-OCT) and electroretinography (ERG) at baseline and 10 years later at the age of 43. The patient also underwent systemic review with detailed cardiac, brain and renal investigations. During follow-up, genetic analysis using whole-exome sequencing was performed on the patient and her parents to identify disease-causing variants.

RESULTS

The patient's main complaint was of a recent onset of bilateral photophobia and blurred vision in the left eye. On examination, the most striking retinal finding was of bilateral well-demarcated, anterior circumferential chorioretinal atrophy with scattered pigment clumping from the mid periphery to the ora. In addition, she had posterior pole RPE hypopigmentation, peripapillary chorioretinal atrophy, left macular choroidal folds and retinal vasculature tortuosity with atypical branching. Her retinal electrophysiology was consistent with a cone rod photoreceptor dystrophy and left macular dysfunction. Ten years later, her BCVA, the anterior circumferential chorioretinal atrophy and her visual field constriction all remained stable. Her retinal electrophysiology demonstrated deterioration of left rod function, while cone dysfunction remained stable. Macular function deteriorated in both eyes. During follow-up, she was also noted to have progressive aortic root dilatation, posterior embryotoxon and an x ray diagnosis of butterfly vertebrae. Whole-exome sequencing revealed a novel c.2412C > A p.(Tyr804Ter) truncating mutation in JAG1 that was predicted to be pathogenic and suggested a diagnosis of Alagille syndrome.

CONCLUSION

This is the first report of the long-term detailed follow-up of a patient with Alagille syndrome whose most striking ophthalmic finding was bilateral well-demarcated, anterior circumferential chorioretinal atrophy. During follow-up, this finding remained stable, suggesting that this may be developmental in origin. This is in contrast with the progressive deterioration in the posterior pole retinal and macular function.

Alagille syndrome and non-syndromic paucity of the intrahepatic bile ducts

The observation of bile duct paucity is an important diagnostic finding in children, occurring in roughly 11% of pediatric liver biopsies. Alagille syndrome (ALGS) is a well-defined syndromic form of intrahepatic bile duct paucity that is accompanied by a number of other key features, including cardiac, facial, ocular, and vertebral abnormalities. In the absence of these additional clinical characteristics, intrahepatic bile duct paucity results in a broad differential diagnosis that requires supplementary testing and characterization. Nearly 30 years after ALGS was first described, genetic studies identified a causative gene, JAGGED1, which spearheaded over two decades of research aimed to meticulously delineate the molecular underpinnings of ALGS. These advancements have characterized ALGS as a genetic disease and led to testing strategies that offer the ability to detect a pathogenic genetic variant in almost 97% of individuals with ALGS. Having a molecular understanding of ALGS has allowed for the development of numerous in vitro and in vivo disease models, which have provided hope and promise for the future generation of gene-based and protein-based therapies. Generation of these disease models has offered scientists a mechanism to study the dynamics of bile duct development and regeneration, and in doing so, produced tools that are applicable to the understanding of other congenital and acquired liver diseases.

Alagille syndrome and risk for hepatocellular carcinoma: Need for increased surveillance in adults with mild liver phenotypes

Alagille syndrome (ALGS) is a multisystem autosomal dominant developmental disorder caused predominantly by pathogenic variants in JAGGED1 (JAG1), and also by pathogenic variants in NOTCH2 in a much smaller number of individuals. Clinical presentation is highly variable and includes liver, heart, eye, skeleton, and facial abnormalities, with a subset of individuals also presenting with kidney, vascular, and central nervous system phenotypes. Hepatocellular carcinoma (HCC) is a rare complication of ALGS, though little is known about its incidence or etiology among affected individuals. Previous reports have identified HCC occurrence in both pediatric and adult cases of ALGS. We present a case report of HCC in a 58‐year‐old woman with a pathogenic JAG1 variant and no overt hepatic features of ALGS. Through a comprehensive literature review, we compile all reported pediatric and adult cases, and further highlight one previously reported case of HCC onset in an adult ALGS patient without any hepatic disease features, similar to our own described patient. Our case report and literature review suggest that ALGS‐causing variants could confer risk for developing HCC regardless of phenotypic severity and highlight a need for a cancer screening protocol that would enable early detection and treatment in this at‐risk population.

Notch Signaling in Skeletal Development, Homeostasis and Pathogenesis

Skeletal development is a complex process which requires the tight regulation of gene activation and suppression in response to local signaling pathways. Among these pathways, Notch signaling is implicated in governing cell fate determination, proliferation, differentiation and apoptosis of skeletal cells-osteoblasts, osteoclasts, osteocytes and chondrocytes. Moreover, human genetic mutations in Notch components emphasize the critical roles of Notch signaling in skeletal development and homeostasis. In this review, we focus on the physiological roles of Notch signaling in skeletogenesis, postnatal bone and cartilage homeostasis and fracture repair. We also discuss the pathological gain- and loss-of-function of Notch signaling in bone and cartilage, resulting in osteosarcoma and age-related degenerative diseases, such as osteoporosis and osteoarthritis. Understanding the physiological and pathological function of Notch signaling in skeletal tissues using animal models and human genetics will provide new insights into disease pathogenesis and offer novel approaches for the treatment of bone/cartilage diseases.

Alagille syndrome mutation update: Comprehensive overview of JAG1 and NOTCH2 mutation frequencies and insight into missense variant classification

Alagille syndrome is an autosomal dominant disease with a known molecular etiology of dysfunctional Notch signaling caused primarily by pathogenic variants in JAGGED1 (JAG1), but also by variants in NOTCH2. The majority of JAG1 variants result in loss of function, however disease has also been attributed to lesser understood missense variants. Conversely, the majority of NOTCH2 variants are missense, though fewer of these variants have been described. In addition, there is a small group of patients with a clear clinical phenotype in the absence of a pathogenic variant. Here, we catalog our single-center study, which includes 401 probands and 111 affected family members amassed over a 27-year period, to provide updated mutation frequencies in JAG1 and NOTCH2 as well as functional validation of nine missense variants. Combining our cohort of 86 novel JAG1 and three novel NOTCH2 variants with previously published data (totaling 713 variants), we present the most comprehensive pathogenic variant overview for Alagille syndrome. Using this data set, we developed new guidance to help with the classification of JAG1 missense variants. Finally, we report clinically consistent cases for which a molecular etiology has not been identified and discuss the potential for next generation sequencing methodologies in novel variant discovery.

Haploinsufficiency of the Notch Ligand DLL1 Causes Variable Neurodevelopmental Disorders

Notch signaling is an established developmental pathway for brain morphogenesis. Given that Delta-like 1 (DLL1) is a ligand for the Notch receptor and that a few individuals with developmental delay, intellectual disability, and brain malformations have microdeletions encompassing DLL1, we hypothesized that insufficiency of DLL1 causes a human neurodevelopmental disorder. We performed exome sequencing in individuals with neurodevelopmental disorders. The cohort was identified using known Matchmaker Exchange nodes such as GeneMatcher. This method identified 15 individuals from 12 unrelated families with heterozygous pathogenic DLL1 variants (nonsense, missense, splice site, and one whole gene deletion). The most common features in our cohort were intellectual disability, autism spectrum disorder, seizures, variable brain malformations, muscular hypotonia, and scoliosis. We did not identify an obvious genotype-phenotype correlation. Analysis of one splice site variant showed an in-frame insertion of 12 bp. In conclusion, heterozygous DLL1 pathogenic variants cause a variable neurodevelopmental phenotype and multi-systemic features. The clinical and molecular data support haploinsufficiency as a mechanism for the pathogenesis of this DLL1-related disorder and affirm the importance of DLL1 in human brain development.

Diagnostic Yield of an Algorithm for Neonatal and Infantile Cholestasis Integrating Next-Generation Sequencing

OBJECTIVE

To evaluate the performance of a diagnostic protocol for neonatal/infantile cholestasis in which the main clinical patterns steered the early use of different genetic testing strategies.

STUDY DESIGN

An observational study was conducted between 2012 and 2017 in a tertiary care setting on a prospective cohort of children with cholestasis occurring at ≤1 year of age and persisting ≥6 weeks, to measure the detection rate of underlying monogenic diseases. After the exclusion of biliary atresia, a clinically driven genetic testing was performed, entailing 3 different approaches with different wideness: confirmatory single-gene testing; focused virtual panels; and wide search through trio whole-exome sequencing.

RESULTS

We enrolled 125 children (66 female, median age 2 months); 96 (77%) patients had hypocholic stools and were evaluated rapidly to exclude biliary atresia, which was the final diagnosis in 74 (59%). Overall, 50 patients underwent genetic testing, 6 with single confirmatory gene testing, 38 through panels, and 6 with trio whole-exome sequencing because of complex phenotype. The genetic testing detection rate was 60%: the final diagnosis was Alagille syndrome in 11, progressive familial intrahepatic cholestasis type 2 in 6, alpha-1-antitrypsin deficiency in 3, and progressive familial intrahepatic cholestasis type 3 in 2; a further 7 genetic conditions were identified in 1 child each. Overall, only 18 of 125 (14%) remained with an indeterminate etiology.

CONCLUSIONS

This protocol combining clinical and genetic assessment proved to be an effective diagnostic tool for neonatal/infantile cholestasis, identifying inherited disorders with a high detection rate. It also could allow a noninvasive diagnosis in children presenting with colored stools.

Alagille Syndrome and the Liver: Current Insights

Alagille syndrome (ALGS) is an autosomal dominant disorder, with multisystem involvement, which usually occurs due to Notch signaling pathway defects, mostly due to JAG1 mutation (ALGS type 1), but rarely due to neurogenic locus notch homolog protein (NOTCH2) mutation (ALGS type 2). It was suspected in cases having at least three out of five major clinical criteria: cholestasis with a paucity of the bile duct, congenital cardiac defects, ocular posterior embryotoxon, typical facial features, and skeletal malformation. Till date, no early predictive marker for hepatic outcome in ALGS has found. No genotypic or, phenotype features or correlation could predict the development of endstage liver disease, which poses a unique management challenge. Cases with progressive liver damage, unremitting cholestasis and intractable pruritus often depend on liver transplantation as last resort. The cardiac, and renal status should be well accessed before liver transplant for the better post-transplantation outcome. Most of the clinical manifestations usually improve the following transplant, except any change in stature. The post liver transplantation outcome was usually comparable with other conditions which require liver transplantation as a last resort, but in this disease the effect of long term immunosuppression on other affected systems not evaluated well till date. Therefore long term post transplant prospective study is required to address these issues.

How to cite this article: Singh SP, Pati GK. Alagille Syndrome and the Liver: Current Insights. Euroasian J Hepatogastroenterol, 2018;8(2):140-147

Notch in skeletal physiology and disease

Notch (Notch1 through 4) are transmembrane receptors that play a fundamental role in cell differentiation and function. Notch receptors are activated following interactions with their ligands in neighboring cells. There are five classic ligands termed Jagged (Jag)1 and Jag2 and Delta-like (Dll)1, Dll3, and Dll4. Recent work has established Notch as a signaling pathway that plays a critical role in the differentiation and function of cells of the osteoblast and osteoclast lineages and in skeletal development and bone remodeling. The effects of Notch are cell-context dependent, and the four Notch receptors carry out specific functions in the skeleton. Gain- and loss-of-function mutations of components of the Notch signaling pathway result in a variety of congenital disorders with significant craniofacial and skeletal manifestations. The Notch ligand Jag1 is a determinant of bone mineral density, and Notch plays a role in the early phases of fracture healing. Alterations in Notch signaling are associated with osteosarcoma and with the metastatic potential of carcinoma of the breast and of the prostate. Controlling Notch signaling could prove useful in diseases of Notch gain-of-function and in selected skeletal disorders. However, clinical data on agents that modify Notch signaling are not available. In conclusion, Notch signaling is a novel pathway that regulates skeletal homeostasis in health and disease.

Alagille Syndrome

Alagille syndrome is a complex multisystem autosomal dominant disorder with a wide variability in penetrance of clinical features. A majority of patients have pathogenic mutations in either the JAG1 gene, encoding a Notch pathway ligand, or the receptor NOTCH2. No genotype-phenotype correlations have been found in any organ system. Liver disease is a major cause of morbidity in this population, whereas cardiac and vascular involvement accounts for most of the mortality. Current therapies are supportive, but the future is promising for the development of targeted interventions to augment Notch pathway signaling in involved tissues.

Clinical and genetic characteristics of 251 consecutive patients with macular and cone/cone-rod dystrophy

Macular and cone/cone-rod dystrophies (MD/CCRD) demonstrate a broad genetic and phenotypic heterogeneity, with retinal alterations solely or predominantly involving the central retina. Targeted next-generation sequencing (NGS) is an efficient diagnostic tool for identifying mutations in patient with retinitis pigmentosa, which shows similar genetic heterogeneity. To detect the genetic causes of disease in patients with MD/CCRD, we implemented a two-tier procedure consisting of Sanger sequencing and targeted NGS including genes associated with clinically overlapping conditions. Disease-causing mutations were identified in 74% of 251 consecutive MD/CCRD patients (33% of the variants were novel). Mutations in ABCA4, PRPH2 and BEST1 accounted for 57% of disease cases. Further mutations were identified in CDHR1, GUCY2D, PROM1, CRX, GUCA1A, CERKL, MT-TL1, KIF11, RP1L1, MERTK, RDH5, CDH3, C1QTNF5, CRB1, JAG1, DRAM2, POC1B, NPHP1 and RPGR. We provide detailed illustrations of rare phenotypes, including autofluorescence and optical coherence tomography imaging. Targeted NGS also identified six potential novel genotype-phenotype correlations for FAM161A, INPP5E, MERTK, FBLN5, SEMA4A and IMPDH1. Clinical reassessment of genetically unsolved patients revealed subgroups with similar retinal phenotype, indicating a common molecular disease cause in each subgroup.

A case of Alagille syndrome presenting with chronic cholestasis in an adult

Alagille syndrome (AGS) is a complex multisystem disorder that involves mainly the liver, heart, eyes, face, and skeleton. The main associated clinical features are chronic cholestasis due to a paucity of intrahepatic bile ducts, congenital heart disease primarily affecting pulmonary arteries, vertebral abnormalities, ocular embryotoxon, and peculiar facies. The manifestations generally become evident at a pediatric age. AGS is caused by defects in the Notch signaling pathway due to mutations in JAG1 or NOTCH2. It is inherited in an autosomal dominant pattern with a high degree of penetrance, but variable expressivity results in a wide range of clinical features. Here we report on a 31-year-old male patient who presented with elevated serum alkaline phosphatase and gamma-glutamyl transpeptidase, and was diagnosed with AGS associated with the JAG1 mutation after a comprehensive workup.

Alagille syndrome: Genetics and Functional Models

Purpose of review

We review the genetics of the autosomal dominant, multi-system disorder, Alagille syndrome and provide a summary on how current functional models and emerging biotechnologies are equipped to guide scientists towards novel therapies. The importance of haploinsufficiency as a disease mechanism will be underscored throughout this discussion.

Recent findings

Alagille syndrome, a human disorder affecting the liver, heart, vasculature, kidney, and other systems, is caused by mutations in the Notch signaling pathway ligand, Jagged1 (JAG1) or the receptor, NOTCH2. Current advances in animal modeling, in vitro cell culture, and human induced pluripotent stem cells, provide new opportunities in which to study disease mechanisms and manifestations.

Summary

We anticipate that the availability of innovative functional models will allow scientists to test new gene therapies or small molecule treatments in physiologically-relevant systems. With these advances, we look forward to the development of new methods to help Alagille syndrome patients.

[Identification of a novel JAG1 mutation in a family affected by Alagille syndrome]

Alagille syndrome (ALGS) is an autosomal dominant disorder which is mainly caused by JAG1 gene mutation and can affect multiple systems including the liver, heart, eyes, skeleton and face. This paper reports the clinical and genetic features of an ALGS patient. A 2-year-and-9-month-old boy was referred to the hospital with the complaint of abnormal liver function and heart murmur discovered over two years. Jaundice of the skin and sclera was not observed. The child had a prominent forehead, left esotropia, depressed nasal bridge and micromandible. The two lungs were clear on auscultation, but a systolic cardiac murmur of grade 2/6 could be heard between the 2nd and 3rd intercostal space at the left sternal border. Neither abdominal distension nor enlarged liver or spleen was discovered. X-ray radiography uncovered butterfly malformation of the 6th and 8th thoracic vertebrae. Serum biochemistry analysis revealed elevation of total bile acids, bilirubin and transaminases. Based on the clinical characteristics and the consultation opinion of the ophthalmologist, the child was diagnosed to have ALGS with Duane retraction syndrome. DNA direct sequencing detected a novel JAG1 mutation c.2419delG(p.Glu807AsnfsX819) in the child. Symptomatic and supportive therapy was performed thereafter and clinical follow-up was conducted until he was 4 years and 2 months. In the follow-up visits, his general condition remained stable, but the facial malformations, left esotropia, cardiac murmur and abnormal liver function persistend. The long-term outcome needed to be observed.

THBS2 Is a Candidate Modifier of Liver Disease Severity in Alagille Syndrome

BACKGROUND & AIMS

Alagille syndrome is an autosomal-dominant, multisystem disorder caused primarily by mutations in JAG1, resulting in bile duct paucity, cholestasis, cardiac disease, and other features. Liver disease severity in Alagille syndrome is highly variable, however, factors influencing the hepatic phenotype are unknown. We hypothesized that genetic modifiers may contribute to the variable expressivity of this disorder.

METHODS

We performed a genome-wide association study in a cohort of Caucasian subjects with known pathogenic JAG1 mutations, comparing patients with mild vs severe liver disease, followed by functional characterization of a candidate locus.

RESULTS

We identified a locus that reached suggestive genome-level significance upstream of the thrombospondin 2 (THBS2) gene. THBS2 codes for a secreted matricellular protein that regulates cell proliferation, apoptosis, and angiogenesis, and has been shown to affect Notch signaling. By using a reporter mouse line, we detected thrombospondin 2 expression in bile ducts and periportal regions of the mouse liver. Examination of Thbs2-null mouse livers showed increased microvessels in the portal regions of adult mice. We also showed that thrombospondin 2 interacts with NOTCH1 and NOTCH2 and can inhibit JAG1-NOTCH2 interactions.

CONCLUSIONS

Based on the genome-wide association study results, thrombospondin 2 localization within bile ducts, and demonstration of interactions of thrombospondin 2 with JAG1 and NOTCH2, we propose that changes in thrombospondin 2 expression may further perturb JAG1-NOTCH2 signaling in patients harboring a JAG1 mutation and lead to a more severe liver phenotype. These results implicate THBS2 as a plausible candidate genetic modifier of liver disease severity in Alagille syndrome.

Alagille syndrome: clinical perspectives

Alagille syndrome is an autosomal dominant, complex multisystem disorder characterized by the presence of three out of five major clinical criteria: cholestasis with bile duct paucity on liver biopsy, congenital cardiac defects (with particular involvement of the pulmonary arteries), posterior embryotoxon in the eye, characteristic facial features, and butterfly vertebrae. Renal and vascular abnormalities can also occur. Inter- and intrafamilial variabilities in the clinical manifestations are common. We reviewed the clinical features and management as well as the molecular basis of Alagille syndrome.

Notch Signaling and the Skeleton

Notch 1 to 4 receptors are important determinants of cell fate and function, and Notch signaling plays an important role in skeletal development and bone remodeling. After direct interactions with ligands of the Jagged and Delta-like families, a series of cleavages release the Notch intracellular domain (NICD), which translocates to the nucleus where it induces transcription of Notch target genes. Classic gene targets of Notch are hairy and enhancer of split (Hes) and Hes-related with YRPW motif (Hey). In cells of the osteoblastic lineage, Notch activation inhibits cell differentiation and causes cancellous bone osteopenia because of impaired bone formation. In osteocytes, Notch1 has distinct effects that result in an inhibition of bone resorption secondary to an induction of osteoprotegerin and suppression of sclerostin with a consequent enhancement of Wnt signaling. Notch1 inhibits, whereas Notch2 enhances, osteoclastogenesis and bone resorption. Congenital disorders of loss- and gain-of-Notch function present with severe clinical manifestations, often affecting the skeleton. Enhanced Notch signaling is associated with osteosarcoma, and Notch can influence the invasive potential of carcinoma of the breast and prostate. Notch signaling can be controlled by the use of inhibitors of Notch activation, small peptides that interfere with the formation of a transcriptional complex, or antibodies to the extracellular domain of specific Notch receptors or to Notch ligands. In conclusion, Notch plays a critical role in skeletal development and homeostasis, and serious skeletal disorders can be attributed to alterations in Notch signaling.

Detection and Quantification of Mosaic Mutations in Disease Genes by Next-Generation Sequencing

The identification of mosaicism is important in establishing a disease diagnosis, assessing recurrence risk, and genetic counseling. Next-generation sequencing (NGS) with deep sequence coverage enhances sensitivity and allows for accurate quantification of the level of mosaicism. NGS identifies low-level mosaicism that would be undetectable by conventional Sanger sequencing. A customized DNA probe library was used for capturing targeted genes, followed by deep NGS analysis. The mean coverage depth per base was approximately 800×. The NGS sequence data were analyzed for single-nucleotide variants and copy number variations. Mosaic mutations in 10 cases/families were detected and confirmed by NGS analysis. Mosaicism was identified for autosomal dominant (JAG1, COL3A1), autosomal recessive (PYGM), and X-linked (PHKA2, PDHA1, OTC, and SLC6A8) disorders. The mosaicism was identified either in one or more tissues from the probands or in a parent of an affected child. When analyzing data from patients with unusual testing results or inheritance patterns, it is important to further evaluate the possibility of mosaicism. Deep NGS analysis not only provides insights into the spectrum of mosaic mutations but also underlines the importance of the detection of mosaicism as an integral part of clinical molecular diagnosis and genetic counseling.

Clinical features, outcomes, and genetic analysis in Korean children with Alagille syndrome

BACKGROUND

Alagille syndrome (AGS) is a multisystem autosomal dominant disorder that affects the liver, heart, eyes, face, bone, and other organs. AGS is caused by mutations in one of two genes, JAG1 or NOTCH2. We evaluated clinical features, outcomes, and the presence of JAG1 and NOTCH2 mutations in Korean children with AGS.

METHODS

Between January 1997 and December 2013, 19 children were diagnosed with AGS at Asan Medical Center, Seoul, Korea. Their clinical features, outcomes, and JAG1 and NOTCH2 mutation status were retrospectively analyzed.

RESULTS

The prevalence of clinical features in the 19 patients was as follows: dysmorphic facial features, 100% (n = 19); liver symptoms, 89% (n = 17); cardiac symptoms, 95% (n = 18); ophthalmologic symptoms, 67% (n = 10); skeletal deformities, 47% (n = 9); and renal symptoms, 21% (n = 4). JAG1 mutations were identified in 14 patients. The 13 different JAG1 mutations, seven of which were novel, included four deletions, three insertions, two missense mutations, three nonsense mutations, and one indel mutation. No NOTCH2 mutations were found. Two patients who received liver transplantation due to liver failure were still alive. Two patients died of comorbidities related to AGS: one of cardiac failure and one of hepatic failure.

CONCLUSION

This study describes the clinical characteristics of 19 Korean AGS patients with seven novel JAG1 mutations. Neonatal cholestatic jaundice was the most common initial presenting symptom; thus the presence of neonatal cholestasis warrants screening for syndromic features of AGS. Complex heart anomalies and progressive liver dysfunction resulted in significant morbidity and mortality in AGS.

Quality of Life and Its Determinants in a Multicenter Cohort of Children with Alagille Syndrome

OBJECTIVES

To assess health-related quality of life (HRQOL) in children with Alagille syndrome (ALGS) in comparison with healthy and other liver disease cohorts, and to identify determinants of HRQOL in patients with ALGS.

STUDY DESIGN

Within the Childhood Liver Disease Research Network prospective study of cholestasis, Pediatric Quality of Life Inventory (PedsQL) questionnaires were administered to 70 children with ALGS, 95 children with alpha-1-antitrypsin deficiency (A1ATD), and 49 children with other causes of chronic intrahepatic cholestasis (IHC) aged 5-18 years. Parent proxy PedsQL scores were recorded for children aged 2-18 years (98 ALGS, 123 A1ATD, and 68 IHC).

RESULTS

Mean ages and total bilirubin (mg/dL) were ALGS 9.4 years; 4.4, A1ATD 9.5 years; 0.7, and IHC 10.3 years; 2.9. ALGS child PedsQL scores were lower than in healthy children and children with A1ATD (mean 73 vs 83; P = .001). Children with ALGS and IHC were similar, except in physical scores (73 vs 79; P = .05). Parents of children with ALGS perceived their children to have worse HRQOL than A1ATD (P ≤ .001) and marginally lower compared with IHC. Univariate analysis revealed ALGS child-reported scores were positively associated with better growth and inversely with total bilirubin. Growth failure, elevated international normalized ratio, and an intracardiac defect were predictive of poor parental scores (P ≤ .05). In multivariate analysis, only weight z-score remained significant for child- and parent-reported scores.

CONCLUSIONS

HRQOL is impaired in children with ALGS compared with healthy and children with A1ATD, similar to children with IHC and is associated with growth failure, which is a potentially treatable cause of impaired HRQOL.

Bile Ducts in Regenerative Liver Nodules of Alagille Patients Are Not the Result of Genetic Mosaicism

Alagille syndrome (ALGS) is a complex, multisystem disease associated with mutations in the JAG1 gene. In the liver, ALGS is characterized by paucity of intrahepatic bile ducts. Gene dosage analysis performed on a large, central regenerative nodule with preserved interlobular bile ducts of 2 unrelated ALGS patients, and on surrounding cirrhotic and ductopenic liver parenchyma, showed in both cases complete JAG1 heterozygous deletion in the regenerative nodule and the ductopenic liver, with no differences in gene dosage. Thus, JAG1 mosaicism and differential haploinsufficiency do not explain the presence of bile ducts in centrally located regenerative nodules.

JAG1 Mutation Spectrum and Origin in Chinese Children with Clinical Features of Alagille Syndrome

Alagille syndrome is an autosomal dominant disorder that results from defects in the Notch signaling pathway, which is most frequently due to JAG1 mutations. This study investigated the rate, spectrum, and origin of JAG1 mutations in 91 Chinese children presenting with at least two clinical features of Alagille syndrome (cholestasis, heart murmur, skeletal abnormalities, ocular abnormalities, characteristic facial features, and renal abnormalities). Direct sequencing and/or multiplex-ligation-dependent probe amplification were performed in these patients, and segregation analysis was performed using samples available from the parents. JAG1 disease-causing mutations were detected in 70/91 (76.9%) patients, including 29/70 (41.4%) small deletions, 6/70 (8.6%) small insertions, 16/70 (22.9%) nonsense mutations, 8/70 (11.4%) splice-site mutations, 6/70 (9.4%) missense mutations, and 5/70 (7.1%) gross deletions. Of the mutations detected, 45/62 (72.6%) were novel, and almost all were unique, with the exception of c.439C>T, c.439+1G>A, c.703C>T, c.1382_1383delAC, c.2698C>T, and c.2990C>A, which were detected in two cases each; three cases exhibited entire gene deletions. A majority (69.2%) of the point and frameshift mutations could be detected by the sequencing of eleven exons (exons 3, 5, 6, 11, 14, 16, 18, 21, and 23-25). The mutation detection rate was 50.0% (10/20) in atypical cases that only presented with two or three clinical features of Alagille syndrome. Segregation analysis revealed that 81.1% (30/37) of these mutations were de novo. In conclusion, JAG1 mutations are present in the majority of Chinese pediatric patients with clinical features of Alagille syndrome, and the mutations concentrate on different exons from other reports. Genetic study is important for the diagnosis of atypical Alagille syndrome in Chinese patients.

Spectrum of JAG1 gene mutations in Polish patients with Alagille syndrome

Alagille syndrome (ALGS) is an autosomal dominant disorder characterized by developmental abnormalities in several organs including the liver, heart, eyes, vertebrae, kidneys, and face. The majority (90-94 %) of ALGS cases are caused by mutations in the JAG1 (JAGGED1) gene, and in a small percent of patients (∼1 %) mutations in the NOTCH2 gene have been described. Both genes are involved in the Notch signaling pathway. To date, over 440 different JAG1 gene mutations and ten NOTCH2 mutations have been identified in ALGS patients. The present study was conducted on a group of 35 Polish ALGS patients and revealed JAG1 gene mutations in 26 of them. Twenty-three different mutations were detected including 13 novel point mutations and six large deletions affecting the JAG1 gene. Review of all mutations identified to date in individuals from Poland allowed us to propose an effective diagnostic strategy based on the mutations identified in the reported patients of Polish descent. However, the distribution of mutations seen in this cohort was not substantively different than the mutation distribution in other reported populations.

Renal involvement and the role of Notch signalling in Alagille syndrome

Alagille syndrome is an autosomal dominant disorder with variable multisystem organ involvement that is caused by mutations in one of two genes in the Notch signalling pathway, JAG1 or NOTCH2. Alagille syndrome is characterized by bile duct paucity, along with at least three of the following features: cholestasis, cardiac defects, skeletal abnormalities, ocular abnormalities and characteristic facies. However, the clinical features of Alagille syndrome are highly variable, and children or adults may also present with predominantly renal findings and little or no hepatic involvement. Renal involvement occurs in 40% of JAG1-mutation-positive individuals. Renal insufficiency is common and has been specifically reported in children with Alagille syndrome who have end-stage liver disease. The role of NOTCH2 and JAG1 in formation of proximal nephron structures and podocytes might explain the observed phenotypes of renal dysplasia and proteinuria in patients with Alagille syndrome, and renal tubular acidosis may be the result of JAG1 expression in the collecting ducts. Renal vascular hypertension in patients with Alagille syndrome is explained by the widespread vasculopathy and the role of Notch signalling in vascular development. Increased awareness of Alagille syndrome amongst nephrologists may lead to more diagnoses of Alagille syndrome in patients with apparently isolated renal disease.

Notch-HES1 signaling axis controls hemato-endothelial fate decisions of human embryonic and induced pluripotent stem cells

Notch signaling regulates several cellular processes including cell fate decisions and proliferation in both invertebrates and mice. However, comparatively less is known about the role of Notch during early human development. Here, we examined the function of Notch signaling during hematopoietic lineage specification from human pluripotent stem cells of both embryonic and adult fibroblast origin. Using immobilized Notch ligands and small interfering RNA to Notch receptors we have demonstrated that Notch1, but not Notch2, activation induced hairy and enhancer of split 1 (HES1) expression and generation of committed hematopoietic progenitors. Using gain- and loss-of-function approaches, this was shown to be attributed to Notch-signaling regulation through HES1, which dictated cell fate decisions from bipotent precursors either to the endothelial or hematopoietic lineages at the clonal level. Our study reveals a previously unappreciated role for the Notch pathway during early human hematopoiesis, whereby Notch signaling via HES1 represents a toggle switch of hematopoietic vs endothelial fate specification.

Notch signaling in skeletal health and disease

Notch receptors are single-pass transmembrane proteins that determine cell fate. Upon Notch ligand interactions, proteolytic cleavages release the Notch intracellular domain, which translocates to the nucleus to regulate the transcription of target genes, including Hairy enhancer of split (Hes) and Hes related to YRPW motif (Hey). Notch is critical for skeletal development and activity of skeletal cells, and dysregulation of Notch signaling is associated with human diseases affecting the skeleton. Inherited or sporadic mutations in components of the Notch signaling pathway are associated with spondylocostal dysostosis, spondylothoracic dysostosis and recessive brachydactyly, diseases characterized by skeletal patterning defects. Inactivating mutations of the Notch ligand JAG1 or of NOTCH2 are associated with Alagille syndrome, and activating mutations in NOTCH2 are associated with Hajdu-Cheney syndrome (HCS). Individuals affected by HCS exhibit osteolysis in distal phalanges and osteoporosis. NOTCH is activated in selected tumors, such as osteosarcoma, and in breast cancer cells that form osteolytic bone metastases. In conclusion, Notch regulates skeletal development and bone remodeling, and gain- or loss-of-function mutations of Notch signaling result in important skeletal diseases.

Alagille Syndrome: A New Missense Mutation Detected by Whole-Exome Sequencing in a Case Previously Found to Be Negative by DHPLC and MLPA

Alagille syndrome (ALGS, MIM 118450) is an autosomal dominant, multisystem disorder with high variability. Two genes have been described: JAG1 and NOTCH2. The population prevalence is 1:70,000 based on the presence of neonatal liver disease. The majority of cases (∼97%) are caused by haploinsufficiency of the JAG1 gene on 20p11.2p12, either due to mutations or deletions at the locus. Less than 1% of cases are caused by mutations in NOTCH2. The most widely used methods for mutational screening include denaturing high-performance liquid chromatography (DHPLC) and multiplex ligation-dependent probe amplification (MLPA). Very recently, whole-exome sequencing (WES) has become technically feasible due to the recent advances in next-generation sequencing technologies, therefore offering new opportunities for mutations/genes identification. A proband and its family, negative for the presence of mutations in JAG1 and NOTCH2 genes by neither DHPLC nor MLPA, were analyzed by WES. A missense mutation, not previously described, in JAG1 gene was identified. This result shows an improvement in the mutation detection rate due to novel sequencing technology suggesting the strong need to reanalyze all negative cases.

Alagille syndrome in a Vietnamese cohort: mutation analysis and assessment of facial features

Alagille syndrome (ALGS, OMIM #118450) is an autosomal dominant disorder that affects multiple organ systems including the liver, heart, eyes, vertebrae, and face. ALGS is caused by mutations in one of two genes in the Notch Signaling Pathway, Jagged1 (JAG1) or NOTCH2. In this study, analysis of 21 Vietnamese ALGS individuals led to the identification of 19 different mutations (18 JAG1 and 1 NOTCH2), 17 of which are novel, including the third reported NOTCH2 mutation in Alagille Syndrome. The spectrum of JAG1 mutations in the Vietnamese patients is similar to that previously reported, including nine frameshift, three missense, two splice site, one nonsense, two whole gene, and one partial gene deletion. The missense mutations are all likely to be disease causing, as two are loss of cysteines (C22R and C78G) and the third creates a cryptic splice site in exon 9 (G386R). No correlation between genotype and phenotype was observed. Assessment of clinical phenotype revealed that skeletal manifestations occur with a higher frequency than in previously reported Alagille cohorts. Facial features were difficult to assess and a Vietnamese pediatric gastroenterologist was only able to identify the facial phenotype in 61% of the cohort. To assess the agreement among North American dysmorphologists at detecting the presence of ALGS facial features in the Vietnamese patients, 37 clinical dysmorphologists evaluated a photographic panel of 20 Vietnamese children with and without ALGS. The dysmorphologists were unable to identify the individuals with ALGS in the majority of cases, suggesting that evaluation of facial features should not be used in the diagnosis of ALGS in this population. This is the first report of mutations and phenotypic spectrum of ALGS in a Vietnamese population.

Notch signaling in human development and disease

Mutations in Notch signaling pathway members cause developmental phenotypes that affect the liver, skeleton, heart, eye, face, kidney, and vasculature. Notch associated disorders include the autosomal dominant, multi-system, Alagille syndrome caused by mutations in both a ligand (Jagged1 (JAG1)) and receptor (NOTCH2) and autosomal recessive spondylocostal dysostosis, caused by mutations in a ligand (Delta-like-3 (DLL3)), as well as several other members of the Notch signaling pathway. Mutations in NOTCH2 have also recently been connected to Hajdu-Cheney syndrome, a dominant disorder causing focal bone destruction, osteoporosis, craniofacial morphology and renal cysts. Mutations in the NOTCH1 receptor are associated with several types of cardiac disease and mutations in NOTCH3 cause the dominant adult onset disorder CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy), a vascular disorder with onset in the 4th or 5th decades. Studies of these human disorders and their inheritance patterns and types of mutations reveal insights into the mechanisms of Notch signaling.